1. Field of the Invention
The subject invention relates to the operation of gas turbine engines, and more particularly, to a control system for positioning compressor inlet guide vanes on a gas turbine engine in such a manner that produces optimized engine transient response.
2. Background of the Related Art
Gas turbine engine for use in rotary wing aircraft, such as helicopters, are typically designed with variable compressor inlet guide vanes (IGVs) which are used in such a manner so as to minimize engine fuel burn. FIGS. 1a and 1b are compressor performance maps illustrating typical compressor performance characteristics as a function of IGV setting, compressor speed and inlet airflow. The variable positioning of the inlet guide vanes allows for optimization of compressor efficiency for a desired engine power level and given air inlet conditions at steady-state conditions. This in turn results in minimized engine fuel burn which is of particular importance at aircraft cruise power conditions.
Modern state-of-the-art digital control systems typically control the positioning of compressor IGV""s according to a normal mode schedule which is illustrated in FIG. 2. The normal mode schedule is typically derived by engine performance engineers and is optimized solely for steady-state engine performance. It would be beneficial however to provide a control strategy for positioning inlet guide vanes during rapid engine accelerations and decelerations in an effort to optimize engine transient response.
The subject invention is directed to a control system controlling the variable positioning of the compressor inlet guide vanes of a gas turbine engine. The system employs a normal mode schedule or map which schedules relatively closed inlet guide vane settings at low compressor speeds and relatively open inlet guide vane settings at high compressor speeds. The normal mode schedule is adapted and configured to optimize engine performance by minimizing fuel burn during steady-state engine operation.
The system further employs an alternate mode schedule or map which schedules inlet guide vane settings that are more closed at low compressor speeds than those scheduled by the normal mode schedule. The alternate mode schedule is adapted and configured to optimize transient engine response during fast engine acceleration.
Control logic is provided for rapidly moving the inlet guide vanes from the more closed settings of the alternate mode schedule to settings that are more open than those scheduled by the normal mode schedule, during an acceleration from low engine power levels. The control logic is further configured to smoothly command the inlet guide vanes back to the settings of the normal mode schedule as the engine acceleration nears completion.
These and other aspects of the subject invention will become more readily apparent to those having ordinary skill in the art from the following detailed description of the invention taken in conjunction with the drawings described hereinbelow.